Shuttle Orbiter Challenger (NASA Designation: OV-99) was a Space Shuttle orbiter constructed using a body frame that had initially been produced for use as a test article.

The Space Shuttle Challenger was destroyed during the launch of mission 51-L on January 28, 1986. An O-Ring seal on the right solid rocket booster began leaking due to a combination of poor inspection and low environmental temperature at the launch site, spraying hot gases onto its attachment point to the main fuel tank and causing structural failure 73 seconds after lift-off[?]. The booster rocket broke free and slammed into the external fuel tank[?], rupturing it. The shuttle stack was then ripped apart by aerodynamic forces[?], and the external tank's fuel ignited into a fireball. Although there is some small evidence that members of the crew may have survived the Shuttle's initial breakup, cabin pressurization[?] was lost and at the altitude where the breakup took place all crewmembers would have died from lack of oxygen before the free-falling crew cabin struck the Atlantic Ocean. On March 9United States Navy divers found the largely intact but heavily-damaged crew compartment with the bodies of all seven astronauts inside.

The Challenger accident caused a long hiatus in shuttle launches: the next mission was not until September 29, 1988 when Discovery set off on mission STS-26[?]. There was also a long investigation into the technical and managerial factors that contributed to the accident; the Shuttle had not been rated to fly in the temperatures of the launch but that concern had been overriden, and the SRB O-rings had been found to be unexpectedly eroded in previous inspections. Reforms to NASA procedures were enacted to prevent another occurrence of such an accident.